1. Field of the Invention
The invention relates to a method and apparatus for cleaning fluid used in an industrial operation, such as a water purification plant, a completion or workover operation of a subterranean well, or the like, wherein a disposable cartridge filter is used to clean the fluid without production of a substantially non-porous solids filter cake around the exterior of the cartridge filter, and to a method of cleaning the cartridge filter utilizing the cleaned fluid in the cleaning procedure.
2. Brief Description of the Prior Art
Disposable cartridge filters are well known to those skilled in the art of cleaning fluids used in industrial operations, such as in municipal waste and water purification operations, refinery and chemical manufacturing operations, food processing procedures, and in the completion and/or workover operations of subterranean oil and/or gas wells. Such disposable cartridge filters generally are formed of a paper-like substance and are designed to be received within a vessel housing same and are removed, disposed of, and replaced with new filters as needed.
In industrial operations wherein a fluid, such as water or the like, is to be cleaned of particulate contaminate matter, such as fine sand, silt, and other similar solids, which is deemed to be a contaminate for one reason or another, a plurality of the cartridge filters will be placed within the vessel and the fluid flow containing the contaminate matter is introduced into the vessel for filtering of the particulate matter around the exterior of the filter, such that the clean fluid passes interiorly through the cartridge filter thence outwardly of the vessel.
When fluids associated with such industrial operations are cleaned incorporating such cartridge filters, a filter cake formed of said particulate matter can be expected to accumulate around the exterior surface of the cartridge filter, and in some events, into the filter media itself, reducing the effectiveness of the cleaning operation and the rate of flow of fluid therethrough and otherwise adversely affecting the filtering operation. As a result of the formation of such filter cake, such cartridge filters must be cleaned or replaced from time to time. Such cleaning or replacement is often time consuming and otherwise costly, resulting in considerable downtime for the flow of fluid during the industrial operation.
In the past, those skilled in the art have attempted to extend the useful life of such disposable cartridge filters by, for example, controlling the pressure of the flow through the filtering system to eliminate or greatly reduce any differential pressure across the cartridge filter exterior face to avoid a buildup of such a non-porous filter cake. Typical of such procedures is that disclosed in U.S. Pat. No. 1,780,723, entitled "Control for Oil Filters", and U.S. Pat. No. 3,926,806, entitled "No-Bypass Filter System".
The present invention provides a method and apparatus for removing particulate matter from fluids circulatable into, through and out of an industrial operation, as well as to a method and apparatus for cleaning of disposable cartridge filters by maintaining a specific minimum flow rate range per filter surface area per minute, as opposed to reducing or eliminating differential pressure across said cartridge filter to provide a substantially non-porous solids filter cake around the exterior of the cartridge filter.
The commonly accepted optimal flow rate through a disposable cartridge filter has thought to be about one-half gallon per square foot per minute, or 1.8925 liters per 144 square inches, or 1,892.5 ml per 144 square inches, which is equal to 13.14 ml per square inch surface area of filter per minute. In contrast, in the present invention, the flow rate across the disposable cartridge filter is maintained at an optimal flow rate. While such flow rate is, of course, dependent upon the construction and other parameters of the selected disposable cartridge filter, the vessel incorporating such filter, and the chemical composition of the fluid to be cleaned therethrough, as well as the volume, particle size and composition of the contaminate particulate matter, typically, such critical flow rate range will be from between about 0.19 ml per square inch of cartridge filter surface per minute to about 1.73 ml per square inch of disposable cartridge filter surface per minute. Preferably, it has been found that such optimal flow rate will be about 0.575 ml per square inch of cartridge filter surface per minute.
By controlling the flow rate through the filter means, particles forming the particulate matter are not effectively carried with the fluid stream and tend to settle out and not be deposited around the exterior of the cartridge filter to thereby be available for the formation of any adverse cake thereacross. Accordingly, any filter cake that develops on the filter media of the disposable cartridge filter is not compressed and does not develop any significant thickness because the force of gravity acting on such cake will be greater than the fluid flow force holding the cake in place. Accordingly, any filter cake that develops will be porous and will retain its permeability and allow the fluid flow rate to be maintained by increasing pump pressure in incremental stages.
In the past, those skilled in the art of incorporating disposable cartridge filters into cleaning operations for industrial applications have encountered considerable problems in cleaning of such cartridge filters upon the occurrence of a buildup of an adverse cake. When such cartridge filters are cleaned by reversing flow of fluid through such filters, the resultant produced dirty fluid must be disposed of in some environmentally acceptable manner. The present invention addresses such problem by providing a system for cleaning of such cartridge filters, in place, incorporating the cleaned fluid produced through normal filtering operation and providing a back flush procedure which does not produce a resultant fluid flow which might be difficult to dispose of because of environmental safeguards.